Title:
Process of installing compliant offshore platforms for the production of hydrocarbons
Kind Code:
A1


Abstract:
To produce hydrocarbons from an offshore production site, a well is drilled into hydrocarbon bearing strata from a non-permanent floating vessel and is then capped. Keying off a template positioned on the well, a base unit is attached to the seabed by driving foundation piles therethrough into the seabed. A tower is installed onto the base unit by attaching lower ends of flex legs of the tower with upper ends of respective foundation piles at locations above the seabed. A deck and topsides are installed to an upper end of the tower. The platform need not be fully compliant until the topsides are installed and operational.



Inventors:
Paulson, Stephen K. (Danville, CA, US)
Will, Stephen A. (Spring, TX, US)
Application Number:
10/944369
Publication Date:
03/16/2006
Filing Date:
09/16/2004
Assignee:
Chevron U.S.A. Inc.
Primary Class:
Other Classes:
166/358
International Classes:
E21B33/043; E21B7/12
View Patent Images:
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Primary Examiner:
BEACH, THOMAS A
Attorney, Agent or Firm:
CHEVRON CORPORATION (SAN RAMON, CA, US)
Claims:
What is claimed is:

1. A process of producing hydrocarbons from a subterranean reservoir beneath a body of water, said process comprising the steps of: A. drilling a well with a non-permanent drilling apparatus; B. positioning a drilling template on a structural casing string of the well; C. finishing the well into hydrocarbon bearing strata; D. capping the finished well and removing the non-permanent drilling apparatus; E. keying off the drilling template to install a production platform extending above the water surface; and thereafter F. operably connecting production equipment of the platform to the finished well for production of hydrocarbons therefrom.

2. The process according to claim 1 wherein step E comprises installing a fully compliant production platform.

3. The process according to claim 1 wherein step E comprises installing a tower extending upwardly past the water surface, mounting a deck onto the tower, and mounting topsides onto the deck, wherein the installed tower is non-fully compliant, and the combination of the tower, the deck, and the operational topsides is fully compliant.

4. The process according to claim 1, wherein step E comprises installing a tower extending upwardly past the water surface, mounting a deck onto the tower, and mounting topsides onto the deck, wherein the installed tower is fully compliant prior to mounting the deck and the topsides.

5. The process according to claim 1 wherein step E includes driving rigid foundation piles through respective guides keyed off the drilling template, and mating flex legs of the tower with respective foundation piles and permanently attaching the flex legs to the foundation piles at respective locations above the seabed and below the water surface.

6. The process according to claim 1 wherein step E further includes keying off the drilling template to install a leveling pile template, driving leveling piles through respective guides of the leveling pile into the seabed, supporting a tower base template on the leveling piles of the leveling pile template, leveling the tower base template using pile shims and/or hydraulic jacks, driving rigid foundation piles through respective guides of the tower base template into the seabed, mating the flex legs of the tower with respective foundation piles, and permanently attaching the flex legs to the foundation piles at a respective locations above the seabed and below the water surface.

7. The process according to claim 6 wherein the leveling pile jacks are retracted after the leveled tower base template is supported by the foundation piles.

8. The process according to claim 1, wherein additional wells are drilled from the platform and completed into hydrocarbon strata subsequent to step B and prior to step F.

9. The process according to claim 1, further including the step of producing hydrocarbons from the formation following step F.

10. The process according to claim 9, further including processing the produced hydrocarbons for uses selected from the group consisting of storage, transportation, further refining, and combinations thereof.

11. A process of installing a compliant offshore platform comprising the steps of: A. attaching a platform base unit to the seabed by driving rigid foundation piles into the seabed; B. mating flex legs of a tower with respective foundation piles and permanently attaching the flex legs to the foundation piles at respective locations above the seabed and below the water surface; and C. installing a tower on the base unit, wherein step A comprises attaching to the seabed a base unit comprised of a drilling template positioned on a pre-drilled well, keying off the drilling template to position a leveling pile template on the seabed, and positioning a tower base template on the leveling pile template and supporting the weight of the tower base template by the leveling piles, and wherein the foundation piles are driven through guides of the tower base template in step A.

12. The process according to claim 11 wherein the leveling pile jacks are retracted after the leveled tower base template is supported by the foundation piles.

13. The process according to claim 12, further including the step of producing hydrocarbons from the formation.

14. The process according to claim 13, further including processing the produced hydrocarbons for uses selected from the group consisting of storage, transportation, further refining, and combinations thereof.

15. The process according to claim 11 wherein the water depth is not greater than 1300 feet.

16. A process of producing hydrocarbons from a subterranean reservoir beneath a body of water having a depth not greater than 1300 feet, said process comprising the steps of: A. drilling a well with a non-permanent drilling apparatus; B. positioning a drilling template on a structural casing string of the well; C. finishing the well into hydrocarbon strata prior or subsequent to step B; D. capping the finished well and removing the non-permanent drilling apparatus; E. installing a production platform on the seabed over the capped well by: C1. attaching a base unit to the seabed, C2. installing a tower on the base unit, thereafter C3. mounting a deck on the tower above the water surface, thereafter C4. attaching topsides to the deck, and thereafter C5. operably connecting production equipment of the platform to the capped well for production of hydrocarbons therefrom; wherein the platform is non-fully compliant following each of steps C1 to C4, and is fully compliant following step C5.

17. The process according to claim 16, further including the step of producing hydrocarbons from the formation.

18. The process according to claim 16 wherein step C1 comprises attaching the base unit to the seabed by driving foundation piles therethrough into the seabed, and step C2 includes mating lower ends of flex legs of the tower to upper ends of respective foundation piles at respective locations above the seabed, and affixing the flex legs to the foundation piles.

19. The process according to claim 18 wherein the leveling pile jacks are retracted after the leveled tower base template is supported by the foundation piles.

20. The process according to claim 11, wherein step A comprises attaching to the seabed a base unit comprised of a leveling pile template on the seabed, and positioning a tower base template on the leveling pile template; wherein the foundation piles are driven through guides of the tower base template in step A.

Description:

FIELD OF THE INVENTION

The present invention generally concerns offshore platforms adapted to have a compliant response to waves, wind and ocean currents, and especially to a process of installing such platforms, as well as to a process of producing hydrocarbons from such platforms.

When installing offshore wells for the production of oil and/or gas (hydrocarbons), the rapidity with which a well can be placed in operation is essential for maximizing overall production and profitability. Making an offshore well operational is an expensive time-consuming task since it requires not only the drilling of the well, but also the installation of a platform from which hydrocarbon extraction and processing operations can be performed.

The installation of platforms in relatively deep water involves more time and expense than in shallower water due to the need to construct a platform that can withstand the considerable forces imposed by waves, wind and currents to which the platform will be subjected. One type of platform that is commonly used in deep water wells is a so-called compliant platform.

Unlike conventional fixed platforms that are designed to resist forces, the compliant platform is designed to flex with the force of waves, wind, and current, i.e., the compliant platform has natural vibration periods which substantially exceed that portion of the range of wave periods representing waves of significant energy, i.e., the predominate wave period. Full compliancy for platform lifetime and safety is considered to be approximately twice the longest periodicity of the waves. Achieving full compliancy in shallower water, i.e., especially for locations with long wave periods poses a challenge. Through the use of its own inertia and flexibility, a compliant platform increases the sway period, thereby reducing the dynamic amplification of the platform's responses to waves, which in turn reduces the structural steel that is needed. Compliant platforms are generally used in water depths of 1000 to 2500 feet. Obtaining the benefits of reduced structural steel for compliant towers at depths in the lower portion of this water depth range requires innovative modifications of traditional compliant tower technology.

Known compliant platforms are disclosed for example in U.S. Pat. Nos. 4,696,603 and 5,988,949.

It is conventional for a compliant platform to include a rigid substructure, or tower, fixed to the ocean bottom with a piled foundation and extending upwardly above the water surface, as disclosed in U.S. Pat. No. 4,696,603. A deck is situated atop the tower. Mounted on the deck are facilities, herein called “topsides,” which contain personnel living quarters, drilling equipment, supplies, and hydrocarbon processing systems, etc.

There is a minimum water depth in which compliant platforms can be used, because of the difficulty involved in achieving full compliancy in the absence of sufficient water depth. That minimum depth will vary as a function of wave velocity, wind intensity, etc., but is generally considered to be about 1000-1300 feet, usually about 1100 feet. The challenges are greatest for locations where wave periods are greater than fifteen seconds at depths less than 1300 feet.

During the installation of compliant offshore platforms, the platform may not achieve full compliancy until near the end of its installation. Because of that, the installation should be completed during a mild weather period, i.e., a period of relatively low wave intensity, to ensure that the substructure is not damaged during installation. In order to ensure that compliancy is achieved during this limited window of opportunity, the platform is designed such that compliancy will be achieved soon after the top of the structure reaches the wave zone, e.g. compliancy is achieved when the substructure has been fully erected, or possibly once the deck, and the topsides have been installed.

The need to expedite the attainment of compliancy has limited the ability to install high-capacity compliant platforms in relatively shallow water whose depth is near the low end of the acceptable range, i.e., when the water depth is about 1000-1300 feet, usually about 1100 feet. In that regard, it will be appreciated that the weight of the “topsides” that is to be supported on the deck increases as drilling/production through-put capacity increases. It would be desirable to enable high-capacity compliant platforms to be installed in relatively shallow water.

It has been heretofore proposed that during the on-shore construction of the compliant platform components, one or more partial wells can be pre-drilled at the offshore production site by means of a floating (non-permanent) drilling vessel, the wells stopping short of the hydrocarbon production zone. Thereafter, the platform is erected at the well site, whereupon the predrilled wells are further drilled into the production zone by drilling equipment disposed on the platform. This need to perform further drilling delays the production of hydrocarbons. Accordingly, room for improvement remains with regard to initiating the extraction of hydrocarbons in an expeditious manner.

SUMMARY OF THE INVENTION

The present invention relates to a process of producing hydrocarbons from a subterranean reservoir beneath a body of water. The process comprises the steps of:

A. drilling a well with a non-permanent drilling apparatus;

B. positioning a drilling template on a structural casing string of the well;

C. finishing the well or wells into hydrocarbon bearing strata;

D. capping the finished well or wells and removing the non-permanent drilling apparatus;

E. keying off the drilling template to install a production platform extending above the water surface; and thereafter

F. operably connecting production equipment of the platform to the capped wellhead for production of hydrocarbons therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become apparent from the following detailed description of a preferred embodiment thereof in connection with the accompanying drawings in which like numerals designate like elements and in which:

FIG. 1 is a schematic view of a drilling vessel drilling a well in a seabed.

FIG. 2 is a schematic view of a capped well with a drilling template mounted thereto.

FIG. 3 is a schematic view similar to FIG. 2 with additional wells drilled through the drilling template. Optionally, a docking pin can be inserted through a spare docking template guide to assist in indexing the leveling pile template.

FIG. 4 is a schematic view similar to FIG. 3 with a leveling pile template being lowered onto the drilling template.

FIG. 5 is a schematic view similar to FIG. 4 after the leveling pile template has been installed onto the drilling template.

FIG. 6 is a schematic view similar to FIG. 5 after leveling piles have been driven through guides of the leveling pile template.

FIG. 7 is a schematic view similar to FIG. 6 showing a tower base template being lowered onto the leveling pile template.

FIG. 8 is a schematic view similar to FIG. 7 after the tower base template has been installed onto the leveling pile template.

FIG. 9 is a schematic view similar to FIG. 8 after foundation piles have been driven through guides of the tower base template, and as a tower bottom section is being lowered onto the tower base template.

FIG. 10 is a schematic view similar to FIG. 9 after the tower bottom section has been lowered onto the tower base template and has been secured thereto.

FIG. 11 is a schematic view similar to FIG. 10 after a tower top section has been lowered onto the tower bottom section.

FIG. 12 is a schematic view similar to FIG. 11 after a deck has been mounted onto the tower top section.

FIG. 13 is a schematic view similar to FIG. 12 after topsides have been mounted onto the deck.

FIG. 14 is a side view of a finished compliant platform according to the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF INVENTION

In accordance with the present invention, the production of hydrocarbons from an offshore well employing a fully compliant offshore drilling and production platform is expedited. That is achieved by making maximum use of the time during which the platform is being built, as well as providing an installation process which expedites the installation of the platform.

As defined herein, an offshore platform is considered as becoming partially compliant when its natural frequency exceeds the predominate wave period, and as becoming fully compliant when its natural frequency is approximately two times the predominate wave period. For example, if the predominate wave period is 12-16 seconds, full compliancy is reached when the natural frequency of the platform reaches about 24-32 seconds.

Depicted in FIG. 1 is a floating drilling vessel V as it installs an initial structural drilling casing of a well 10A into the seabed S. (typically 100 to 300 feet into the seabed). FIG. 2 depicts a drilling template 12 being mounted on the initial drilling casing of the well 10A. Subsequently, the well 10A can be fully drilled all the way into the hydrocarbon strata and is capped off and protected by a cap 11. Either before or after the well 10A is drilled to the hydrocarbon strata H, structural casing string(s) for one or more additional wells (10B, 10C, etc) can be batch installed through the template by means of the drilling vessel (see FIG. 3). Those optional additional wells 10B, 10C are also drilled all the way into the hydrocarbon strata and are capped off. Some of these wells can be directional wells, i.e., horizontal delineation wells within the hydrocarbon-producing strata. The drilling template 12 is left in place for reasons to be discussed. Optionally, a docking pin 13 can be inserted through the drilling template to help index the leveling pile template.

During the period in which the wells 10A-C are being drilled, the components of a compliant offshore platform are being constructed at an onshore site and will eventually be transported to the production site.

Prior to the arrival of the major platform components at the production site, a leveling pile template 14 is lowered onto the drilling template 12 by stabbing two or more male pins 14A of the leveling pile template into respective female guides 12D of the drilling template, as shown in FIGS. 4-5. Alternatively, the male/female mating guides and pins can be reversed and/or mixtures thereof can be used to mate the drilling template and the leveling pile template.

Leveling piles 16 are then installed into the seabed 29 through guides 18 of the leveling pile template as shown in FIG. 6. All of the leveling piles 16 will have their tops located at about the same elevation. Shims 26 can be mounted on one or more of the leveling piles so that the tops of the leveling piles 16 are at a proper and level elevation (accuracy is approximately ±0.1 degrees).

A tower base template 20 is then lowered and mounted on the leveling pile template 14 by mating male posts 22 of the tower base template into respective female stabbing guides 24 of the leveling pile template, as shown in FIGS. 7-8. Alternatively, the male/female mating guides and pins can be reversed and/or mixtures thereof can be used to mate the leveling template and the tower base template. The tower base template 20 carries conventional adjustable hydraulic jacks 25 that rest on respective leveling piles 16 to support the weight of the tower base template. The jacks 25 can then be activated to additionally level the tower base template if required, i.e., to achieve vertically of the tower base template. Any suitable means can be employed to achieve verticality, but a combination of shims and jacks is preferred.

Then, rigid foundation piles 28 are installed through guides 30 of the tower base template 20 and driven into the seabed substantially below the mudline, as shown in FIG. 8. Pile penetrations below mudline can be in excess of 300 feet or more depending on foundation soil type and strength.

The unit comprised of the non-weight bearing drilling template 12, the leveling pile template 14, which is also not weight bearing at tower completion, and the tower base template 20, situated above the seabed, which constitutes a unit 39 to which a platform tower is to be installed. After the grouting or affixing of the foundation piles and flex legs, the tower base template and tower base section merely hang therefrom.

In an alternative embodiment, the platform is installed and the hydrocarbons are produced from a compliant platform of the invention positioned above the sea floor in accordance with the invention in the absence of pre-drilling wells and drilling template and the employment of the leveling pile template, the tower base template, tower bottom section and the tower top section and subsequent drilling and well completion.

Installation of the remaining platform tower is initiated by lowering a tower bottom section 32 onto the tower base template 20 whereby flex legs 34, already attached to the tower bottom section, stab over the respective foundation piles 28 (see FIG. 10). No vertical load is transferred to the foundation piles at this point. The tower bottom section is checked for levelness. If required, the hydraulic jacks 25 between the tower bottom section and leveling piles are activated to level the tower within specified tolerances (typically ±0.1 degrees). The flex legs 34 included with the tower bottom section are then attached to the foundation piles 28 by grouting 36 over a specified length. This attachment location between flex legs and foundation piles is about 100 feet above the ocean floor 29. Grouted connections 36 are made between the tower bottom section 32 and the tower base template 20 as shown in FIG. 10. Beyond this time point, the hydraulic jacks 25 are retracted, to eliminate contact between the tower bottom section 32 and the leveling piles, so that the weight of the tower bottom section 32 and tower base template 20 are fully supported only by the foundation piles 28. Decoupling the leveling piles helps to achieve a longer sway period.

Thereafter, at least one additional tower section, including a tower top section 40 is lowered onto the tower bottom section 32, as shown in FIG. 11. Grouted connections 42 are made between the tower top section 40 and the tower bottom section 32 at locations below the water surface.

In lieu of the preferred use of grouting, other conventional means could be employed to attach the flex legs 34 to the foundation piles 28, or the tower sections to one another, such as swaging, mechanical fasteners, and welding for example.

The combination feature wherein the flex legs are attached to foundation piles above the seabed is different from a flex pile driven in the ocean bed and offers significant advantages as compared to the prior art practice of driving the flex legs into the seabed. It will be appreciated that long flexible legs cannot be driven into soil as efficiently as stiffer foundation piles, due to the greater axial flexibility of longer piles. Because of this, flex legs cannot be driven into the seabed as far as the foundation piles, so a greater number of flex legs must be used than would otherwise be the case. That increases the time and expense required for installation. In addition, as explained above and further below, the foundation flex pile combination is mechanically different from a flex pile directly driven into the ocean bed.

Separately installed foundation piles can be optimally sized for load bearing capacity versus time after driving. This allows the flex legs to be sized for the proper combination of flexibility and strength to assist tuning the platform compliant response to the desired sway period.

Furthermore, the foundation piles can be driven in advance of installing the tower sections 32, 40 so they will have sufficient time to set-up (cure) within the soil prior to the tower sections are being installed. Consequently, since the load-bearing capacity of the foundation piles increases with time after having been driven, the piles will be able to reach acceptable design values prior to the installation of the remaining tower sections, the deck, and the topsides. This provides a benefit not available where the flex piles are driven in substantially in concert and time with the tower section being installed.

The upper ends of the flex legs 34 terminate at a location somewhat below the water surface to insure compliant behavior (e.g. platform natural sway period approximately two times the predominate wave period) of the fully installed tower, deck, and operational topsides. In shallow water the depth of the flex leg to the tower connection can be shallower than required in deeper water depths.

Once installed, the tower top section 40 extends upwardly past the water surface.

Thereafter, a deck 50 is installed on the top of the tower top section in conventional fashion, as shown in FIG. 12. Importantly, the thusfar-described decked tower 60 comprised of the top and bottom tower sections 40, 32 plus the deck 50, need not be fully compliant. In order to be fully compliant, the natural vibration period of the structure should exceed the range of the predominate wave period by approximately two times that range. For compliant towers located in the shallower range of water depths in which compliant towers are typically installed, the tower may not be fully compliant prior to the installation of the deck, topsides, and produced hydrocarbon fluids. Preferably, however, it is only after the completion of the platform (see FIG. 13), i.e., after the remaining components 70 of the platform, herein called the “topsides”, are mounted on the deck, that the platform becomes fully compliant. By “topsides” is meant such things as for example, personnel living quarters, drilling derricks, hydrocarbon extraction and processing systems and supplies and equipment therefore. Consequently, the addition of the topsides will cause the natural frequency of the completed platform to be approximately two times the predominate wave periodicity.

The feature wherein the platform is not fully compliant prior to the installation of the deck, topsides and produced hydrocarbon fluids enables a greater weight to be added to the tower without over-loading the completed platform and foundations. That means that the platform can be used for high-capacity production operations in relatively shallow water.

It will be appreciated that if the tower is not compliant without the added weight of the installed and/or operational topsides, then the tower design process must include appropriate allowances for temporary non-compliant tower performance during the platform installation sequence. This design allowance typically involves insuring foundation pile loadings and tower structural strength and fatigue damage are within acceptable design limits prior to installation of the topsides. This feature is achieved by optimization of the foundation pile and flex leg design combination because of the higher load capacities achievable with separately preinstalled foundation piles.

Once the platform has been fully installed, the extraction and processing systems of the topsides are connected to the pre-drilled wells 10A-C by suitable tie-back connections, production tubing installed, and the hydrocarbon production is initiated.

It will be appreciated that the depiction of the platform 70 in FIG. 13 is schematic and not to scale. A completed platform is shown more to scale in FIG. 14. To characterize one example of installing a compliant platform in shallow water, if one were to assume a water depth of 1280 ft., then the top of the drilling template could be at a depth of 1271 ft. below the water surface; the upper ends of the foundation piles 28 disposed outside of the flex piles 34 could be 100 ft. above the mudline (i.e., at a depth of about 1180 feet); the top of the tower bottom section 32 could be at a depth of 390 ft. The connection between the tops of the flex legs and the tower bottom section 32 is at a depth more than intermediate between the mudline and the wave zone or about 490 ft., so such connection would be at about 62% of the distance from the seabed to the water surface.

The present invention provides a number of advantages. Since the pre-drilled well(s) 10A-C are drilled all the way to the production formation prior to the installation of the tower, no additional drilling into the hydrocarbon stratum is required in order to commence production. Following the tower and topsides installation, the pre-drilled wells are tied back using well conductors lowered through the tower and stabbed over the pre-drilled wells 10A, 10B, and 10C. The platform can commence production operations after appropriate completion tubing strings are installed inside the pre-drilled well casings and connected to the topside extraction and production equipment.

The installation of the compliant platform is facilitated by keying the installation off of the drilling template 12. That is, the drilling template 12 serves as a guide for locating the leveling pile template which, in turn, locates the tower base template 20.

The leveling pile template 14 and associated leveling piles 16 serve to ensure that the tower located thereabove is properly leveled, e.g., through the use of shims and/or hydraulically adjustable devices.

The platform is secured to the seabed, not directly by flex legs, but by foundation piles 28 which are driven into the soil through guides of the tower base template 20. The flex legs 28 are pre-mounted on the tower bottom section 32 and are vertically aligned with the upper ends of respective rigid foundation piles 28 to which they are stabbed over and subsequently connected by grouting. There is no transfer of weight of the tower sections to the foundation piles at this point (the weight is supported by the leveling piles 16), so the grouting procedure is facilitated.

Hydraulic grippers can be used to temporarily affix the flex legs to the foundation piles during installation. Hydraulic grippers can also be used at the other connection interfaces (e.g. tower base template and tower bottom section, and tower bottom section and tower top section) as required for platform installation stability.

For a compliant tower installed in 1280 foot water depth, the tubular foundation piles 28 would typically have a total length of about 500 to 600 feet, and exhibit penetrations below mudline of approximately 400 to 500 feet. Also, the piles 28 would be formed of higher strength steel tubular shapes with typical diameters of 7 to 10 feet, and wall thicknesses of 2 to 4 inches. The appropriate number of foundation piles is determined during the design process, but typically would include two to four piles at each of the four tower corners. The flex legs are about 730 ft. in length and are formed of higher strength steel tubular shapes with typical diameters of 7 to 10 feet, and with typical wall thicknesses of 1.5 to 2.5 inches. It will be appreciated that driving a unitary flex pile over 1200 or 1300 feet long requires a multiple pile section installation rather than single pile section installation, has reduced pile drivability, and cannot be installed in advance to permit maximum pile capacity to develop prior to tower installation. The foundation piles and flex legs in the preferred configuration are provided in clusters of equal numbers at each corner of the tower. Thus, there could be three foundation piles (and three flex legs) at each of four corners, for a total of twelve foundation piles and twelve flex legs.

Advantages of the above-described preferred configuration include the following.

    • 1) Tower fabrication can be split into more manageable sized sections that can be fabricated at different world-wide fabrication locations if required.
    • 2) The building-block stacking of the various tower sections (drilling template, leveling pile template, leveling piles, tower base template, foundation piles, tower bottom section, and tower top section) provides an effective framework for adapting the compliant tower to various site conditions. Some of these site conditions would include water depth, topside weight, and oceanographic design criteria.
    • 3) The foundation piles can be pre-installed prior to the installation of the remainder of the tower sections. This allows the foundation pile capacity, which increases with time after pile driving, to reach acceptable design values prior to installation of the remaining tower sections and topsides. This avoids the need to over-design the pile capacity for an immediately acceptable load capacity.
    • 4) The ability to install long single-piece foundation piles with improved pile drivability and resulting larger pile capacities is possible. This is contrasted with previous compliant tower concepts that where only the flex legs were the structural foundation component. Because of their longer length and higher flexibility those prior art flex legs had lower pile drivability.
    • 5) The stacked configuration allows the platform levelness to be checked and corrected to design tolerances at several different installation time steps. Insuring the proper levelness (or verticality) of the compliant tower is mandatory to the proper performance of the tower system.

Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims. For example, in any instances where it is indicated that male portions of various parts are stabbed into female guides of other parts, it will be appreciated that the male/female components can be on either of the parts being joined, or there can be a mixing thereof wherein a given part includes both male and female components or other suitable mechanical connections can be employed. In addition, any suitable leveling means can be used to obtain design required levelness.